1. Field of the Invention
The present invention relates generally to a suspension control system for an automotive vehicle which utilizes variable damping force shock absorbers for suppressing nose-dive and/or squatting motion of a vehicle body when starting or braking as well as vertical vibrations during parking.
2. Description of the Prior Art
Japanese Patent First Publication No. 61-75007 discloses a suspension control system for controlling damping characteristics of shock absorbers. This system is operable to monitor depression of an accelerator pedal during traveling at a speed below a preselected value by means of vehicle speed, selector position, throttle opening, and longitudinal acceleration sensors for enhancing damping characteristics of the front shock absorbers in an extension or rebounding stroke and of the rear shock absorbers in a compression or bounding stroke when the depression of the accelerator pedal is over a preselected degree. With this damping characteristic modification, squatting motion of the vehicle body which may be caused by sudden acceleration of the vehicle while traveling at a relatively low speed is restricted.
However, since the above conventional suspension control system is responsive to signals from the various sensors indicative of a degree of depression of the accelerator pedal to modify the damping force characteristics of the shock absorbers, a time lag occurs between detection and a time when the damping force characteristics of the shock absorbers are actually modified, resulting in squatting motion of the vehicle body not being suppressed sufficiently when the vehicle starts quickly after being parked.
Additionally, Japanese Patent First Publication No. 63-305014 discloses a suspension control system which is adapted for suppressing nose-dive of a vehicle body during braking. This system projects vertical vibrational force acting on the vehicle body based on damping force of shock absorbers. When the projected vibrating force is less than a preselected threshold value, the shock absorbers are controlled to assume harder damping force characteristics, while above the threshold value, softer damping force characteristics are provided. Additionally, the system monitors braking operation when the shock absorbers are oriented to the softer damping force characteristics. If the vehicle is in braking operation, the shock absorbers are controlled to exhibit the harder damping force characteristics for suppressing nose-dive of the vehicle body and reaction therefrom when the vehicle stops.
However, such prior art suspension control systems encounter a drawback in that, during parking of the vehicle after braking operation, the system may be responsive to vertical motion of the vehicle body due to passengers getting in and/or out of the vehicle so as to switch the damping force characteristics of the shock absorbers unnecessarily, thereby causing power consumption to be increased as well as causing the shock absorbers to become degraded prematurely.